Seven Marines were killed and at least eight others were injured when a powerful 60mm mortar exploded in a tube during a training exercise in Nevada, the Marines said today.

The Marines have issued a suspension on the use of all 60mm mortars and their associated tubes while they conduct a review of what caused a round to explode. The suspension will affect mortars used both in training and in deployed settings.

The Marines, who were from the 2nd Marine Division based at Camp Lejeune, N.C., were conducting live fire maneuver training at the Hawthorne Army Depot 140 miles southeast of Reno, Nev., Monday when Lukeman said it appeared a mortar round exploded in a tube at 9:55 p.m. MT.

One sailor was among the injured in the blast, Brig. Gen. Jim Lukeman said today.

A Defense official later told ABC News that the sailor was a Navy corpsman working with the unit. It was not clear where the Marines were standing or the cause of the blast, which Lukeman said is under investigation.

The survivors are being treated at Renown Regional Medical Center in Reno for injuries that include trauma fractures and vascular injuries, hospital spokeswoman Stacy Kendall told ABC News.

Two Marines and one sailor are very seriously injured, while three Marines have serious injuries and a seventh Marine was treated for minor injuries, Lukeman said.

The Marines had been training at the Hawthorne Army Depot and the nearby Mountain Warfare Training Center for the past month, Lukeman said. The training was not in anticipation of an imminent deployment, he said.

The mountainous desert terrain of the 230-square-mile depot is used as a training location for special forces since it "provides a realistic simulation of the situation in Afghanistan," according to the depot's website. The depot is also used as a storage site for ammunition awaiting demilitarization.

It takes several Marines to fire a 60mm mortar and they must "work together to provide constant and accurate high-angle suppressive fire," according to the Marines' website.

The mortar the Marines were using is a "lightweight company mortar fired from a stationary position," Lukeman said.

The Marine Corps is notifying families before releasing the identities of those who were killed. Lukeman said the names would be made public 24 hours after all the next of kin were notified.

"Our first priority is to provide them the support they need during this very difficult time," he said.